This invention relates to the field of substrate processing. More particularly the invention relates to a highly automated system for locating precise positions on a substrate surface.
At a very basic level, the method by which semiconductor devices are made involves just a very few steps that are repeated over and over again until the device is formed. For the purposes of this discussion, these steps fall into three basic categories: deposition of a layer of material on the existing substrate, patterning of a layer of material, and removal of a portion of a layer of material. While there are certainly many other steps involved with semiconductor fabrication, and many variations on those recited above, these three steps tend to be the basis of microelectronic processing.
In all three of the steps mentioned, thickness measurements are critically important. For example, layers of material are deposited to desired thicknesses and a desired thickness of photoresist is typically used to pattern the layers of material. The third general step, removing a portion of the layer of the material, can be further resolved into two general categories, either thinning or planarizing the entire layer or removing the entire thickness of the layer in specific locations. The importance of accurate measurement of the thickness of the layer cannot be overstated when thinning a layer to the desired thickness.
There are several reasons why a layer may need to be thinned to a specific thickness. One reason, briefly alluded to above, is to planarize the layer. In a planarization process, the portions of the layer that are relatively higher than the lower portions of the layer are selectively thinned, thus producing a more generally level top surface for the layer. One way to planarize or otherwise thin a layer is to abrade the surface of the wafer against a pad. Water or some other liquid can be introduced during the abrasion process to help carry away the material that is removed from the layer as it wears against the pad. In addition, other materials such as grit or chemical etchants can be added to the water to increase either the rate or the uniformity of the thinning action.
It is helpful to measure the thickness of a layer at some point prior to beginning a thinning process so that an initial determination can be made as to how long the wafer should be subjected to the thinning process. Additionally, it is helpful to make intermediate measurements during the thinning process so that the layer is not thinned excessively. Thus, measurement of the thickness of the layer plays an important role in this process.
As many as fifty or more layers may need to be processed in the manner described above in order to produce some integrated circuits. In addition, the wafer fab producing the devices may process thousands of different devices. Typically, each layer must be measured at a different location on the surface of the wafer. Further, each of the different devices produced will tend to have measurement locations in a different position. Thus, many thousands of different locations for layer thickness measurement may need to be identified and tracked.
While the position on the wafer for each of these thousands of measurement locations could be manually located by an operator using a microscope, and the measurements manually taken after the measurement location is individually located, such a system would tend to be fraught with the mistakes that are prone to occur when a person performs a repetitive task selected from thousands of different repetitive tasks.
What is needed, therefore, is a system that automates portions of the thickness measurement process, so that at least some of the errors produced by human mistakes can be eliminated.
The above and other needs are met by a system for precisely locating an absolute position of a target structure disposed at a known relative position on a substrate, where the substrate has devices in a pattern. Input means receive information, including a substrate size, a pattern offset, a device size, the known relative position of the target structure, and a target structure shape. Staging means receive the substrate in a known orientation.
Processing means are used to locate several positions. A center position of the substrate is located from the substrate size and the known orientation of the substrate. A first intermediate position is located by combining the center position of the substrate with the pattern offset. A second intermediate position is located by combining the first intermediate position with at least a first component of the device size. A third intermediate position is located by combining the second intermediate position with the known relative position of the target structure.
The absolute position of the target structure is located by comparing the target structure shape to shapes of structures disposed on the substrate in proximity to the third intermediate position, and aligning the target structure shape to a closest matching one of the structures disposed in proximity to the third intermediate position.
Thus, the absolute position of the target structure is determined by using physical data, such as the size of the substrate and the known orientation of the substrate, data relating to the devices that are patterned on the substrate, including device size, and relative data, such as the general location of the target structure within the device. In this manner, an operator can quickly program a substrate position location system that can receive a wafer and find a position on the wafer that is close enough to the absolute position of the target structure on the die, that the absolute position of the target structure can be found with techniques such as small field pattern recognition. By inputting data of this type, the operators tend to make fewer mistakes in programming systems, such as metrology systems, as to where to take thickness measurements. Reducing these types of errors also tends to reduce the number of wafers that are scrapped or reworked, thus lowering costs.
There are many preferred embodiments of the system described above, as briefly mentioned below. In one, the processing means locates the third intermediate position by combining the substrate size, the known orientation of the substrate, the pattern offset, at least the first component of the device size, and the known relative position of the target structure, without independently locating the center position of the substrate, the first intermediate position, and the second intermediate position.
Positioning means dispose the absolute position of the target structure adjacent a test zone. Measurement means measure within the test zone a thickness of a layer of material on the substrate within the target structure.
Further, the processing means include means for locating a plurality of absolute positions of the target structure by combining the third intermediate position with multiples of the device size to produce a plurality of closely approximated positions. The processing means locate the plurality of absolute positions of the target structure by comparing the target structure shape to shapes of structures disposed in proximity to the closely approximated positions, and aligning the target structure shape to a closest matching one of the structures disposed in proximity to each of the closely approximated positions.
Also described is a method for precisely locating an absolute position of a target structure disposed at a known relative position on a substrate having devices in a pattern. Information is input to a processing means. The information includes a substrate size, a pattern offset, a device size, the known relative position of the target structure, and a target structure shape. The substrate is received in a known orientation.
A center position of the substrate is located from the substrate size and the known orientation of the substrate, using the processing means. A first intermediate position is located by combining the center position of the substrate with the pattern offset using the processing means. A second intermediate position is located by combining the first intermediate position with at least a first component of the device size using the processing means. A third intermediate position is located by combining the second intermediate position with the known relative position of the target structure using the processing means.
The absolute position of the target structure is located by comparing the target structure shape to shapes of structures disposed on the substrate in proximity to the third intermediate position, and aligning the target structure shape to a closest matching one of the structures disposed in proximity to the third intermediate position.